Radiation detectors, having an array of pixels, are applied in, for example, CT imaging systems, to provide a sufficiently accurate measure of the radiation incident on the detector after it has left a scanned object. The use of easy to manufacture semiconductor material, such as silicon, for the radiation detector is beneficial in view of for example costs, compared to, for example, Cd(Zn)Te as a sensor material. Although Cd(Zn)Te has a much higher stopping power than silicon and exhibits much less Compton scatter resulting in inter-pixel crosstalk, Cd(Zn)Te shows significant K-fluorescence, which deteriorates the energy resolution and can also cause inter-pixel crosstalk. Furthermore, Cd(Zn)Te is an expensive material, difficult to manufacture in large sizes and, due to its brittleness, exhibits limitations as to layer thicknesses. In contrast, the K-fluorescence in radiation detectors based on a semiconductor material, such as silicon, is negligible. While silicon is almost transparent for upper X-ray energies (round 100 keV), photon energies below 35 keV are well absorbed. However, for medium photon energies a high probability for Compton scatter exists, which alters the photon direction as well as its energy, giving rise to spatial and spectral crosstalk between neighbouring and further away pixels. Also in contrast to Cd(Zn)Te, semiconductor based radiation detectors can profit from an experienced and well-known semiconductor technology routinely used in industry.
One major disadvantage of such a semiconductor based radiation detector is the amount of crosstalk between pixels, mainly due to Compton scatter, that reduces the image quality. This is the case for any relevant pixel size, since Compton scattered photons traverse far distances up to the range of centimeters within silicon and therefore easily induce spatial crosstalk between pixels which are not adjacent.
JP59064587 discloses a radiation detector for reducing the crosstalk between adjacent radiation detectors caused by radioactive rays scattering on the radiation detectors in an X-ray CT unit. Semiconductor radiation detectors and signal-takeout mounts are fixed onto a collimator board made of a metal with a high capability to stop radioactive rays. The collimator board, while attenuating the effect the scattering of radioactive rays between adjacent radiation detectors, functions as a negative electrode which greatly reduces crosstalk between adjacent radiation detectors caused by scattered radioactive rays. A disadvantage of this radiation detector is that only cross-talk is reduced between adjacent radiation detectors and not between the pixels of each radiation detector. Furthermore, it requires a complicated fabrication process in which the radiation detectors are mounted on a collimator board that reduces the crosstalk between the radiation detectors.